Magnets and magnetic systems, particularly such comprising NdFeB-magnets, must generally be protected from corrosion. This requires an appropriate coating, e.g., a lacquering.
In the structure of magnetic systems the magnets are connected to each other and/or other work pieces, such as steel back irons or other magnetically soft work pieces, by way of adhesion. Here, it is required that the adhesive connection shows high stability, preferably ≧10 N/mm2 in connection to a high temperature resistance. For example, temperatures up to 180° C. develop in applications in motors and high opposing fields act upon the magnets. The adhesion must withstand such conditions.
In the so-called segmented magnetic systems composed from several individual magnets the system is fixed and held together by way of adhesion. The cured adhesive film furthermore has the function to electrically insulate the individual magnets from each other. A good electric insulation is necessary because such systems are used in large electrically operating machines, such as marine engines, wind generators, etc. and the electric insulation of the individual magnets prevents the occurrence of strong eddy currents and thus the engine from overheating.
When producing magnetic systems usually the process includes that the magnets are adhered with the help of liquid high-performance adhesives, such as epoxy resins, acrylates, etc. Subsequently the magnetic systems are coated with a corrosion protection to protect the systems from the environment and the influences of chemicals. Here, generally enamel is used, however frequently the problem occurs that in the area of the adhesion gap faulty enamel sections appear, which are caused by enclosed gas and/or air bubbles.
This problem can be avoided in that the corrosion protection is applied prior to the adhesion, which however disadvantageously adds another processing step for each individual magnet.
Attempts have been made to perform the production of the corrosion protection as well as the adhesion of the magnets in a single processing step. However it has shown that the lacquers used here cannot fully comply with the requirements of some systems. For example, when standard lacquers on a phenol-resin base are used comprising additional fillers, such as aluminum or zinc or corrosion protection pigments, the required insulation properties for segmented systems are not achieved. Furthermore, brittleness develops in such systems in extended high-temperature aging. In standard epoxy resin lacquers it has been found that the adhesive strength is insufficient at high temperatures.